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Purpletop vervain is a short-lived perennial from South America that grows with a highly distinctive upright and open habit. Clusters of light purple flowers occur in late spring on 3-6 ft. tall branches that often ascend above other plants in the garden. This unique perennial grows well throughout the Inland Empire in sunny locations and with low amounts of supplemental water. It is combined with other flowering perennials and butterfly plants in mixed plantings, along borders and in small masses.

Water Needs

Purpletop vervain grows well in Inland Empire gardens in areas of full sun and with low amounts of summer water. The chart shown below provides a recommended baseline guide to the monthly irrigation schedule and volume of supplemental water needed to maintain healthy growth throughout the average year. It should be noted there are several months indicated by an asterisk (*) when winter rains can provide sufficient moisture and irrigation is not needed. The high and low range of moisture indicates it can grow with varying amounts of water and you should make irrigation adjustments based on field observations of growth and character; greater moisture during the spring sustains a longer flowering season.

Irrigation Schedule and Graph

Low Water Use Plants

Irrigation Schedule 2

  Jan* Feb* Mar* Apr May Jun Jul Aug Sep Oct Nov* Dec*
Runs per Month 0x to 2x 0x to 2x 0x to 2x 1x to 2x 1x to 2x 1x to 2x 1x to 2x 1x to 2x 1x to 2x 1x to 2x 0x to 2x 0x to 2x
Inches per Run 1" 1" 1" 1" 1" 1" 1" 1" 1" 1" 1" 1"
Inches per Month 0" to 2" 0" to 2" 0" to 2" 1" to 2" 1" to 2" 1" to 2" 1" to 2" 1" to 2" 1" to 2" 1" to 2" 0" to 2" 0" to 2"

Range of supplemental summer water: 7"-14"
Range of supplemental winter water: 0"-10"

  Jan* Feb* Mar* Apr May Jun Jul Aug Sep Oct Nov* Dec*
For more information on how to use this Irrigation Schedule and Graph, follow this link.

For information how to calculate your irrigation system’s schedule and precipitation rate, please follow this link.

Plant Properties

Plant Type: Perennial
Foliage Character: Evergreen
Habit: Upright, Open
Growth Rate: Short-lived, Fast
Height: 3 ft. - 6 ft.
Width: 3 ft.
Water Needs: Low 2
Foliage Color: Medium green
Flower Color: Lavender
Flower Season: Spring
Soil Adaptations: Well-draining soil, Clay
Exposure Adaptations: Heat, Frost, Drought, Aridity, All day sun
Function: Wildlife value, Flowering accent plant, Borders, Banks, Attracts butterflies


Prune out spent flower stalks or leave them on to develop mature seeds if you want Verbena bonariensis to lightly seed itself around the garden. After blooming, plants flower stalks along with leaves will eventually begin to look leggy and ragged. When this happens, cut almost all the way to the ground, leaving just a few buds at the base of the plant. Plants will grow back reinvigorated. At certain times of the year, these plants often develop a white fungus on the leaves called powdery mildew. In general, there is no need to resort to fungicides, as the plants are simply prone to the infection and can usually survive it with no problems. If the powdery mildew is significant, simply cut back to the base, as explained above, to remove infested parts of the plants and stimulate new growth. It is best to throw out mildew infested material rather than compost it or keep it on site as part of the mulch layer. Good air circulation around plants and keeping foliage dry helps discourage powdery mildew (S).



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